When the yachts are idle, which is the majority of the time, they are typically plugged into shore power and are thus just consuming electricity from the grid. The electrical systems of these things are typically far more efficient than your home because they must generate their own electricity when at sea.
As for the wasting of money, you'll note that most of the cost of building a yacht is labor because they are mostly one-off builds and can't take advantage of automation. The article mentions that they cost 10% of the purchase price per month in upkeep. The vast majority of those costs are labor.
These things are among the most efficient devices for transferring wealth from the rich to the middle class. I wouldn't discourage their use at all.
I also wonder how much of the yacht business is really about money laundering or tax-evasion. Like the art collecting world. If your company buys the boat in one country, reflags it to Panama, sells it in Monaco the next tax year... I don't know any details but I'm sure there's substantial room here to massage what numbers you present to various tax collectors.
Indeed, it's pretty hard to tell. Both seem entirely plausible and I just have no way to guess how such buyers think.
Realistically speaking, are these areas lacking money? Will throwing more money at the problem solve it, or is it another one of those "nine women can't make a baby in one month" problems?
Really, I find it hard to care about what other people do with their own time, effort or money. I'm not trying to stan billionaires, but really, who cares that they bought a yacht?
These could consume the wealth of several billionaires, make a difference to hundreds of thousands of individuals, and still not make much of a visible dent in the scope of the problems.
Also, depending on the problem you're trying to solve, "hundreds of thousands of individuals" could very well constitute your entire problem space.
The real question though, is why not both? Most people buying super yachts could probably afford to set up a philanthropic fund of some kind.